Low concentrations of pesticides are in streams and ground
water throughout the nation. At least one pesticide was
detected in more than 95 percent of stream samples collected
at 115 sites.

Concentrations of individual pesticides in samples were
almost always below current U.S. Environmental Protection
Agency (USEPA) drinking-water standards.

Nearly two-thirds of all streams sampled had at least
one pesticide at a concentration exceeding a guideline for
the protection of aquatic life.

What do these findings mean?
These findings do not necessarily translate into effects on
human or aquatic health. USGS can detect these chemicals in
very small amounts that are 10 to 100 times below the threshold
used for setting standards and guidelines. These low-level
detections allow scientists to identify and evaluate emerging
issues and to track contaminant levels over time.

It is difficult to assess the potential risk to humans and
to aquatic life from these chemicals. No standards or guidelines
exist for many pesticides and their breakdown
products. Guidelines to protect aquatic life have been
developed for only 18 of the 88
pesticides NAWQA analyzes for; drinking-water standards
or health advisory levels have been developed for only 52.
In addition, these criteria have been developed for individual
chemicals and do not account for exposure to chemical mixtures
or to the high concentrations that occur in seasonal "pulses."
And the potential effects on reproductive, nervous, and immune
systems, as well as on chemically sensitive individuals, are
not well understood.

How USEPA and the States use NAWQA pesticide data
USEPA Office of Pesticides uses USGS data for pesticide registration
and for assessments of pesticide exposure. One of the performance
goals of the Office of Pesticides states:

By 2010, detections of the 15 pesticides most frequently
found in surface water in USGS 1994 NAWQA data will be reduced
by 50 percent. Any new pesticides registered since 1996
found in USGS 2010 data for surface water will have a detection
frequency no greater than 30 percent. By 2010, 50 percent
of all pesticides with the potential to leach to ground
water will be managed through labeling or other methods
to prevent ground-water contamination.

USGS also provides USEPA with

ancillary data, such as on geology, hydrology, and land
use, needed to interpret the monitoring data

Pesticides
in Ground Water--Summary Statistics; Results of
the National Water Quality Assessment Program (NAWQA),
1992-1998 and Pesticides
in Streams--Summary Statistics; Results of the National
Water Quality Assessment Program (NAWQA), 1992-1998